1. Field of Invention
The present invention relates to improved fuel cell assemblies for generating power, and more particularly to improved sealing structures applied to individual fuel cell plates secured together via bolted connections.
2. Description of the Prior Art
It is known to apply resilient sealing beads to the faces of fuel cell plates for control of fluid flows between a plurality of such plates stacked and bolted together for such purpose. In a typical fuel cell arrangement, pluralities of such plates are sandwiched together in a parallel, face-to-face pattern during the conventional assembly of a fuel cell apparatus. The plates are held spaced apart by resilient sealing beads adhesively bonded to the face of at least one of any two adjoining plates. The sealing beads define paths or channels for fluids to flow between the plates, and thus fluid electrolytes are used to transfer energy in this manner as will be appreciated by those skilled in the art.
The cell plates employed in the usual fuel cell are brittle, as they are typically formed of composites that include graphite. Thus, special care must be taken with respect to the handling of the plates during fuel cell construction, manufacture, or repair to assure that the brittle plates will not be damaged or compromised. Such care extends even to the post-manufacture handling of the fuel cell to avoid physically bending or cracking of the brittle plates.
The brittleness issue is particularly exacerbated by the use of bolted connections through apertures distributed about the periphery of the stacked plates. In such cases the apertures may be spaced significant distances from intermediate areas of the plates that contain the fluid sealing beads adapted to control flows of electrolytes between the plates. Thus, the torquing of the bolted connections for securement of the plates together may actually introduce bending moments in the plates, as the intermediately positioned fluid sealing beads tend to counteract the tightening of bolts about the peripheral edges of the plates. Such moments tend to eventually lead to cracking of the brittle plates, particularly during any postmanufacturing handling of fuel cell structures, as noted.
The present invention provides an improved fuel cell plate construction, wherein sealing bead thickness is controlled over the surface area of the plate, including those areas about bolt apertures used for securing the plates together, in an effort to alleviate over-stressing or cracking of the normally brittle plates. Thus, a plurality of parallel, stacked plates which incorporate the present invention are separated by a plurality of discrete sealing beads disposed over at least one of any two facing plates. In a preferred form, the sealing beads are applied to the faces of the plates by screen-printing techniques to produce accurate thicknesses. The sealing beads are resilient, preferably formed of an elastomeric material, and have varied thicknesses or plate surface heights to accommodate variations in stress levels produced when such plates are bolted together under conventional fuel cell manufacturing techniques. Thus, upon installation of a plurality of fuel cell plates together via bolted connections, the beads are adapted to maintain desired separations between the stacked plates.
To the extent that the highest localized stress areas typically occur in regions immediately adjacent bolt apertures, this invention provides for sealing beads of lower heights or thicknesses about the bolt apertures than for the fluid sealing beads spaced away from the bolt apertures and normally adapted to accommodate fluid flows. In the same preferred embodiment, the sealing beads about the bolt apertures are wider, though of lesser thickness, than the fluid sealing beads. Thus, the fuel cell plates of this invention have compensating thicknesses and widths of the sealing beads about the bolt apertures relative to fluid sealing beads that share the same plate, in order to minimize stress fractures and related premature deterioration of the fuel cell plates.